Optical recording medium, method for manufacturing the same and target used for sputtering process

ABSTRACT

An optical recording medium includes a recording layer containing an alloy represented by a general formula: (Ti x M 1   x ) y M 2   y , where element M 1  is Si or Al, element M 2  is an element selected from the group consisting of Si, Al and Fe and different from the element M 1 , x is equal to or larger than 0.3 and equal to or smaller than 0.8, and y is equal to or larger than 0.75 and equal to or smaller than 1. 
     The thus constituted optical recording medium only places minimal load on the global environment.

BACKGROUND OF THE INVENTION

The present invention relates to an optical recording medium, a methodfor manufacturing an optical recording medium and a target used for asputtering process and, particularly, to an optical recording mediumincluding a recording layer formed of materials that place minimal loadon the global environment, a method for manufacturing such an opticalrecording medium, and a target used for a sputtering process thatenables a recording layer of an optical recording medium to be formed ofmaterials that place minimal load on the global environment.

DESCRIPTION OF THE PRIOR ART

Optical recording media such as the CD, DVD and the like have beenwidely used as recording media for recording digital data. These opticalrecording media can be roughly classified into optical recording mediasuch as the CD-ROM and the DVD-ROM that do not enable writing andrewriting of data (ROM type optical recording media), optical recordingmedia such as the CD-R and DVD-R that enable writing but not rewritingof data (write-once type optical recording media), and optical recordingmedia such as the CD-RW and DVD-RW that enable rewriting of data (datarewritable type optical recording media).

Data are generally recorded in a ROM type optical recording medium usingprepits formed in a substrate in the manufacturing process thereof,while in a data rewritable type optical recording medium a phase changematerial is generally used as the material of the recording layer anddata are recorded utilizing changes in an optical characteristic causedby phase change of the phase change material.

On the other hand, in a write-once type optical recording medium, anorganic dye such as a cyanine dye, phthalocyanine dye or azo dye isgenerally used as the material of the recording layer and data arerecorded utilizing changes in an optical characteristic caused bychemical change of the organic dye, which change may be accompanied byphysical deformation.

Unlike data recorded in a data rewritable type optical recording medium,data recorded in a write-once type optical recording medium cannot beerased and rewritten. This means that data recorded in a write-once typeoptical recording medium cannot be falsified, so that the write-oncetype optical recording medium is useful in the case where it isnecessary to prevent data recorded in an optical recording medium frombeing falsified.

However, since an organic dye is degraded when exposed to sunlight orthe like, it is difficult to improve long-time storage reliability inthe case where an organic dye is used as the material of the recordinglayer. Therefore, it is desirable for improving long-time storagereliability of the write-once type optical recording medium to form therecording layer of a material other than an organic dye.

As disclosed in Japanese Patent Application Laid Open No. 62-204442, anoptical recording medium including two recording layers formed ofinorganic materials is known as an example of an optical recordingmedium whose recording layer is formed of a material other than anorganic dye.

However, the inorganic materials for forming recording layers of theoptical recording medium disclosed in Japanese Patent Application LaidOpen No. 62-204442 include materials which place a heavy load on theenvironment so that the optical recording medium disclosed in JapanesePatent Application Laid Open No. 62-204442 does not satisfy therequirement for protecting global atmosphere.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalrecording medium including a recording layer formed of materials whichplace minimal load on the global environment.

It is another object of the present invention to provide a method formanufacturing an optical recording medium including a recording layerformed of materials which place minimal load on the global environment.

It is a further object of the present invention is to provide a targetlo used for a sputtering process, which can form a recording layer of anoptical recording medium of materials which place minimal load on theglobal environment.

The above and other objects of the present invention can be accomplishedby an optical recording medium comprising a recording layer containingan alloy represented by a general formula: (Ti_(x)M1 _(1−x))_(y)M2_(1−y), where element M1 is Si or Al, element M2 is an element differentfrom the element M1, x is equal to or larger than 0.3 and equal to orsmaller than 0.8, and y is equal to or larger than 0.75 and equal to orsmaller than 1.

Since each of Ti, Si and Al contained in the recording layer is one ofthe most commonplace elements on earth and puts only an extremely lightload on the global environment, the optical recording medium including arecording layer containing an alloy containing such elements that isprovided by the present invention can greatly lower the load placed theglobal environment.

According to the present invention, when a laser beam is projected ontothe recording layer of the optical recording medium, the alloy containedin the recording layer as a primary component is melted at a region ofthe recording layer irradiated with the laser beam and the phase of thealloy is changed when the melted alloy is solidified, thereby recordingdata in the recording layer.

In the present invention, it is necessary for x defining the content ofTi and the element M1, namely, Si or Al in the alloy contained in therecording layer, to be equal to or larger than 0.3 and equal to orsmaller than 0.8. In a study done by the inventors of the presentinvention, it was found that in the case where x was smaller than 0.3 orx exceeded 0.8, it was impossible to obtain a reproduced signal having ahigh C/N ratio and jitter of the reproduced signal and cross-talk ofdata became worse.

In a further study done by the inventors of the present invention, itwas found that the recording characteristic of the optical recordingmedium improved as the content of the element M2 decreased and when ywas equal to 1, in other words when the recording layer consisted of analloy of Ti and Si or an alloy of Ti and Al, the recordingcharacteristic of the optical recording medium became best.

In the present invention, in order to obtain a reproduced signal havinga higher C/N ratio and more effectively suppress cross-talk of data, itis preferable for x to be equal to or larger than 0.4 and equal to orsmaller than 0.6 and it is particularly preferable for x to be about0.5.

In the present invention, it is preferable for the element M2 in theabove mentioned general formula to be selected from the group consistingof Si, Al and Fe.

Since each of Si, Al and Fe contained in the alloy as an optionalcomponent is one of the most commonplace elements on earth and puts onlyan extremely light load on the global environment, an optical recordingmedium including a recording layer containing as a primary component analloy containing such elements can greatly lower the load placed theglobal environment.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a dielectric layer on at least one side of therecording layer.

According to this preferred aspect of the present invention, since therecording layer is physically and chemically protected by the dielectriclayer, degradation of recorded data can be effectively prevented over along period.

In a further preferred aspect of the present invention, the opticalrecording medium further comprises dielectric layers on opposite sidesof the recording layer.

The inventors of the present invention further vigorously pursued astudy for accomplishing the above and other objects and, as a result,made the discovery that when a recording layer of an optical recordingmedium was formed by a sputtering process using a target containing analloy represented by a general formula: (Ti_(x′)M1 _(1−x′))_(y′)M2_(1−y′), where element M1 is Si or Al, element M2 is an elementdifferent from the element M1, x′ is equal to or lager than 0.37 andequal to or smaller than 0.85 and y′ is equal to or lager than 0.75 andequal to or smaller than 1, it was possible to form a recording layercontaining an alloy represented by the general formula: (Ti_(x)M1_(1−x))_(y)M2 _(1−y), where element M1 is Si or Al, element M2 is anelement different from the element M1, x is equal to or larger than 0.3and equal to or smaller than 0.8, and y is equal to or larger than 0.75and equal to or smaller than 1.

Therefore, the above and other objects of the present invention can bealso accomplished by a target used for a sputtering process thatcontains an alloy represented by a general formula: (Ti_(x′)M1_(1−x′))_(y′)M2 _(1=y′), where element M1 is Si or Al, element M2 is anelement different from the element M1, x′ is equal to or lager than 0.37and equal to or smaller than 0.85 and y′ is equal to or lager than 0.75and equal to or smaller than 1.

According to this aspect of the present invention, it is possible tofabricate an optical recording medium which can reproduce a signalhaving a high C/N ratio and low jitter, can effectively suppresscross-talk of data and has an improved recording sensitivity.

In the present invention, it is preferable for the element M2 in theabove mentioned general formula to be selected from the group consistingof Si, Al and Fe.

The above and other objects of the present invention can be alsoaccomplished by a method for manufacturing an optical recording mediumcomprising of a step of forming a recording layer of an opticalrecording medium by a sputtering process using a target that contains analloy represented by a general formula: (Ti_(x′)M1 _(1−x′))_(y)M2_(1=y′), where element M1 is Si or Al, element M2 is an elementdifferent from the element M1, x′ is equal to or lager than 0.37 andequal to or smaller than 0.85 and y′ is equal to or lager than 0.75 andequal to or smaller than 1.

According to the present invention, it is possible to fabricate anoptical recording medium which can reproduce a signal having a high C/Nratio and low jitter, can effectively suppress cross-talk of data andhas an improved recording sensitivity.

The above and other objects and features of the present invention willbecome apparent from the following description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cutaway perspective view showing anoptical recording medium that is a preferred embodiment of the presentinvention.

FIG. 2 is an enlarged schematic cross-sectional view of the part of theoptical recording medium indicated by A in FIG. 1.

FIG. 3 is a diagram showing the waveform of a pulse train pattern formodulating the power of a laser beam in the case of recording 2T signalsin a recording layer of an optical recording medium shown in FIGS. 1 and2.

FIG. 4 is a diagram showing the waveform of a pulse train pattern formodulating the power of a laser beam in the case of recording 3T signalsin a recording layer of an optical recording medium shown in FIGS. 1 and2.

FIG. 5 is a diagram showing the waveform of a pulse train pattern formodulating the power of a laser beam in the case of recording 4T signalsin a recording layer of an optical recording medium shown in FIGS. 1 and2.

FIG. 6 is a diagram showing the waveform of a pulse pattern formodulating the power of a laser beam in the case of recording one amonga 5T signal to an 8T signal in a recording layer of an optical recordingmedium shown in FIGS. 1 and 2.

FIG. 7 is a schematic cross-sectional view showing an optical recordingmedium which is another preferred embodiment of the present invention.

FIG. 8 is a graph showing how a C/N ratio of a signal reproduced fromeach of optical recording medium samples #1-1 to #1-5 varied with avalue of x.

FIG. 9 is a graph showing how single jitter and cross jitter of a signalreproduced from each of optical recording medium samples #1-1 to #1-5varied with a value of x.

FIG. 10 is a graph showing how a C/N ratio of a signal reproduced fromeach of optical recording medium samples #3-1 to #3-4 varied with avalue of y.

FIG. 11 is a graph showing how single jitter and cross jitter of asignal reproduced from each of optical recording medium samples #3-1 to#3-4 varied with a value of y.

FIG. 12 is a graph showing how a C/N ratio of a signal reproduced fromeach of optical recording medium samples #5-1 to #5-5 varied with avalue of x.

FIG. 13 is a graph showing how single jitter and cross jitter of asignal reproduced from each of optical recording medium samples #5-1 to#5-5 varied with a value of x.

FIG. 14 is a graph showing how a C/N ratio of a signal reproduced fromeach of optical recording medium samples #7-1 to #7-3 varied with avalue of y.

FIG. 15 is a graph showing how single jitter and cross jitter of asignal reproduced from each of optical recording medium samples #7-1 to#7-3 varied with a value of y.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic partially cut perspective view showing an opticalrecording medium that is a preferred embodiment of the present inventionand FIG. 2 is a schematic enlarged cross-sectional view indicated by Ain FIG. 1.

As shown in FIG. 1, an optical recording medium 10 according to thisembodiment is formed disk-like and has an outer diameter of about 120 mmand a thickness of about 1.2 mm.

An optical recording medium 10 according to this embodiment isconstituted as a write-once type optical recording medium and as shownin FIG. 2, it includes a support substrate 11, a reflective layer 12formed on the surface of the support substrate 11, a second dielectriclayer 13 formed on the surface of the reflective layer 12, a recordinglayer 14 formed on the surface of the second dielectric layer 13, afirst dielectric layer 15 formed on the surface of the recording layer14 and a light transmission layer 16 formed on the surface of the firstdielectric layer 15.

In this embodiment, as shown in FIG. 2, a laser beam L having awavelength of 380 nm to 450 nm is projected onto a light incidence plane16 a constituted by one surface of the light transmission layer 16,thereby recording data in the optical recording medium 10 or reproducingdata from the optical recording medium 10.

The support substrate 11 serves as a support for ensuring mechanicalstrength and a thickness of about 1.2 mm required for the opticalrecording medium 10.

The material used to form the support substrate 11 is not particularlylimited insofar as the support substrate 11 can serve as the support ofthe optical recording medium 10. The support substrate 11 can be formedof glass, ceramic, resin or the like. Among these, resin is preferablyused for forming the support substrate 11 since resin can be easilyshaped. Illustrative examples of resins suitable for forming the supportsubstrate 11 include polycarbonate resin, polyolefin resin, acrylicresin, epoxy resin, polystyrene resin, polyethylene resin, polypropyleneresin, silicone resin, fluoropolymers, acrylonitrile butadiene styreneresin, urethane resin and the like. Among these, polycarbonate resin andpolyolefin resin are most preferably used for forming the supportsubstrate 11 from the viewpoint of easy processing, opticalcharacteristics and the like and in this embodiment, the supportsubstrate 11 is formed of polycarbonate resin. In this embodiment, sincethe laser beam L is projected via the light incident plane 16 a locatedopposite to the support substrate 11, it is unnecessary for the supportsubstrate 11 to have a light transmittance property.

As shown in FIG. 2, grooves 11 a and lands 11 b are alternately andspirally formed on the surface of the support substrate 11 so as toextend from a portion in the vicinity of the center of the supportsubstrate 11 toward the outer circumference thereof or from the outercircumference of the support substrate 11 toward a portion in thevicinity of the center thereof. The grooves 11 a and/or lands 11 b serveas a guide track for the laser beam L.

The depth of the groove 11 a is not particularly limited and ispreferably set to 10 nm to 40 nm. The pitch of the grooves 11 a is notparticularly limited and is preferably set to 0.2 μm to 0.4 μm.

The reflective layer 12 serves to reflect the laser beam L enteringthrough the light transmission layer 16 so as to emit it from the lighttransmission layer 16.

The material used to form the reflective layer 12 is not particularlylimited insofar as it can reflect a laser beam L, and the reflectivelayer 12 can be formed of Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ge, Ag,Pt, Au and the like. Among these materials, it is preferable to form thereflective layer 12 of a metal material having a high reflectioncharacteristic, such as Al, Au, Ag, Cu or alloy containing at least oneof these metals, such as alloy of Ag and Cu.

The reflective layer 12 also serves to increase the difference inreflection coefficient between a recorded region and an unrecordedregion by a multiple interference effect, thereby obtaining a higherreproduced signal (C/N ratio).

The thickness of the reflective layer 12 is not particularly limited butis preferably from 5 nm to 300 nm, more preferably from 20 nm to 200 nm.

In the case where the thickness of the reflective layer 12 is thinnerthan 5 nm, it is difficult to reflect a laser beam L in a desiredmanner. On the other hand, in the case where the thickness of thereflective layer 12 exceeds 300 nm, the surface smoothness of thereflective layer 12 becomes worse and it takes a longer time for formingthe reflective layer 12, thereby lowering the productivity of theoptical recording medium 10.

The first dielectric layer 15 and the second dielectric layer 13 serveto protect the recording layer 14. Degradation of recorded data can beprevented over a long period by the first dielectric layer 15 and thesecond dielectric layer 13.

The material for forming the first dielectric layer 15 and the seconddielectric layer 13 is not particularly limited insofar as it istransparent in the wavelength range of the laser beam L and the firstdielectric layer 15 and the second dielectric layer 13 can be formed ofa dielectric material containing oxide, sulfide, nitride, carbide or acombination thereof, for example, as a primary component. In order toprevent the support substrate 11 from being deformed by heat and improvethe characteristics of the first dielectric layer 15 and the seconddielectric layer 13 for protecting the recording layer 14, it ispreferable to form the first dielectric layer 15 and the seconddielectric layer 13 of an oxide, sulfide, nitride or carbide of Al, Si,Ce, Ti, Zn, Ta or the like, such as Al₂O₃, AlN, ZnO, ZnS, GeN, GeCrN,CeO, CeO₂, SiO, SiO₂, Si₃N₄, SiC, La₂O₃, TaO, TiO₂, SiAlON (mixture ofSiO₂, Al₂O₃, Si₃N₄ and AlN), LaSiON (mixture of La₂O₃, SiO₂ and Si₃N₄)or the like, or the mixture thereof.

The first dielectric layer 15 and the second dielectric layer 13 may beformed of the same dielectric material or of different dielectricmaterials. Moreover, at least one of the first dielectric layer 15 andthe second dielectric layer 13 may have a multi-layered structureincluding a plurality of dielectric films.

The first dielectric layer 15 and the second dielectric layer 13 alsoserve to increase the difference in optical properties of the opticalrecording medium 10 between before and after data recording and it istherefore preferable to form the first dielectric layer 15 and thesecond dielectric layer 13 of a material having a high refractive indexn in the wavelength range of the laser beam L. Further, since therecording sensitivity becomes low as the energy absorbed in the firstdielectric layer 15 and the second dielectric layer 13 becomes largewhen the laser beam L is projected onto the optical recording medium 10and data are to be recorded therein, it is preferable to form the firstdielectric layer 15 and the second dielectric layer 13 of a materialhaving a low extinction coefficient k in the wavelength range of thelaser beam L.

In view of the above, it is particularly preferable to form the firstdielectric layer 15 and the second dielectric layer 13 of a mixture ofZnS and SiO₂ whose mole ratio is 80:20.

The thickness of the first dielectric layer 15 and the second dielectriclayer 13 is not particularly limited but is preferably from 3 nm to 200nm. If the first dielectric layer 15 or the second dielectric layer 13is thinner than 3 nm, it is difficult to obtain the above-describedadvantages. On the other hand, if the first dielectric layer 15 or thesecond dielectric layer 13 is thicker than 200 nm, it takes a long timeto form the first dielectric layers 15 and the second dielectric layers13, thereby lowering the productivity of the optical recording medium10, and cracks may be generated in the first dielectric layers 15 and/orthe second dielectric layers 13 owing to stress present in the firstdielectric layers 15 and/or the second dielectric layer 13.

The recording layer 14 is adapted for forming a record mark andrecording data therein.

In this embodiment, the recording layer 14 contains an alloy representedby a general formula: (Ti_(x)M1 _(1−x))_(y)M2 _(1−y) where element M1 isSi or Al, element M2 is an element different from the element M1, x isequal to or larger than 0.3 and equal to or smaller than 0.8, and y isequal to or larger than 0.75 and equal to or smaller than 1.

The recording characteristic of the optical recording medium 10 improvesas the content of the element M2 decreases and when y is equal to 1, inother words when the recording layer 14 consists of an alloy of Ti andSi or an alloy of Ti and Al, the recording characteristic of the opticalrecording medium 10 becomes best.

However, it is necessary for x defining the content of Ti and Si or Tiand Al in the alloy to be equal to or larger than 0.3 and equal to orsmaller than 0.8. In the case where x is smaller than 0.3 or x exceeds0.8, it is impossible to obtain a reproduced signal having a high C/Nratio and jitter of the reproduced signal and cross-talk of data becomeworse.

In order to obtain a reproduced signal having a higher C/N ratio andmore effectively suppress cross-talk of data, it is preferable for x tobe equal to or larger than 0.4 and equal to or smaller than 0.6 and itis particularly preferable for x to be about 0.5.

Preferably, the element M2 in the above mentioned general formula isselected from the group consisting of Si, Al and Fe.

Since each of Ti, Si and Al contained as an indispensable component inthe alloy contained in the recording layer 14 and Si, Al and Fecontained in the alloy as an optional component is one of the mostcommonplace elements on earth and puts only an extremely light load onthe global environment, an optical recording medium 10 including arecording layer 14 containing an alloy containing such elements cangreatly lower the load placed the global environment.

As the thickness of the recording layer 14 increases, the recordingsensitivity becomes worse and since the amount of a laser beam Labsorbed in the recording layer 14 increases, the reflective coefficientis lowered. Therefore, it is preferable make the recording layer thinnerin order to prevent the recording sensitivity from becoming worse andthe reflective coefficient from being lowered, but in the case where thethickness of the recording layer 14 is too small, the change inreflection coefficient between before and after irradiation with thelaser beam L is small, so that a reproduced signal having high strength(C/N ratio) cannot be obtained. Moreover, it becomes difficult tocontrol the thickness of the recording layer 14.

Therefore, it is preferable to form the recording layer 14 to have athickness of 3 nm to 40 nm and more preferable to form it to have athickness of 5 nm to 30 nm.

The light transmission layer 16 serves to transmit a laser beam L andpreferably has a thickness of 10 μm to 300 μm. More preferably, thelight transmission layer 16 has a thickness of 50 μm to 150 μm.

The material used to form the light transmission layer 16 is notparticularly limited but in the case where the light transmission layer16 is to be formed by the spin coating process or the like, ultravioletray curable resin, electron beam curable resin or the like is preferablyused. More preferably, the light transmission layer 16 is formed ofacrylic ultraviolet ray curable resin or epoxy ultraviolet ray curableresin.

The light transmission layer 16 may be formed by adhering a sheet madeof light transmittable resin to the surface of the first dielectriclayer 15 using an adhesive agent.

The optical recording medium 10 having the above-described configurationcan, for example, be fabricated in the following manner.

The support substrate 11 having grooves 11 a and lands 11 b on thesurface thereof is first fabricated by an injection molding processusing a stamper.

The reflective layer 12 is then formed on the surface of the substrate11 formed with the grooves 11 a and lands 11 b.

The reflective layer 12 can be formed by a vapor growth process usingchemical species containing elements for forming the reflective layer12. Illustrative examples of the vapor growth processes include vacuumdeposition process, sputtering process and the like but it is preferableto form the reflective layer 12 using the sputtering process.

The second dielectric layer 13 is then formed on surface of thereflective layer 12.

The second dielectric layer 13 can be also formed by a vapor growthprocess using chemical species containing elements for forming thesecond dielectric layer 13. Illustrative examples of the vapor growthprocesses include vacuum deposition process, sputtering process and thelike but it is preferable to form the second dielectric layer 13 usingthe sputtering process.

The recording layer 14 is then formed on the second dielectric layer 13.

The recording layer 14 can be formed by a vapor growth process using analloy containing at least Ti and one of Si and Al. Illustrative examplesof the vapor growth processes include the vacuum deposition process,sputtering process and the like but it is preferable to form the seconddielectric layer 13 using the sputtering process.

The inventors of the present invention conducted a study that led to adiscovery regarding a recording layer 14 of an optical recording medium10 formed by a sputtering process using a target containing an alloycontaining at least Ti and one of Si and Al. Specifically, the inventorsdiscovered that when the target contains an alloy represented by ageneral formula: (Ti_(x′)M1 _(1−x′))_(y′)M2 _(1−y′), where x′ is equalto or lager than 0.37 and equal to or smaller than 0.85 and y′ is equalto or lager than 0.75 and equal to or smaller than 1, a recording layer14 containing an alloy represented by the above mentioned generalformula: (Ti_(x)M1 _(1−x))_(y)M2 _(1−y) can be formed.

Such a target can be fabricated by mixing powder of Ti and powder of oneof Si and Al and baking the mixed powder, for example.

The first dielectric layer 15 is then formed on the recording-layer 14.The first dielectric layer 15 can be also formed by a gas phase growthprocess using chemical species containing elements for forming the firstdielectric layer 15.

Finally, the light transmission layer 16 is formed on the firstdielectric layer 15. The light transmission layer 16 can be formed, forexample, by applying an acrylic ultraviolet ray curable resin or epoxyultraviolet ray curable resin adjusted to an appropriate viscosity ontothe surface of the second dielectric layer 15 by spin coating to form acoating layer and irradiating the coating layer with ultraviolet rays tocure the coating layer.

Thus, the optical recording medium 10 was fabricated.

In the case where data are to be recording in the optical recordingmedium 10 of the above-described configuration, a laser beam L whosepower is modulated is projected onto the recording layer 14 via thelight transmission layer 16, while the optical recording medium 10 isbeing rotated.

In order to record data with high recording density, it is preferable toproject a laser beam L having a wavelength λ of 450 nm or shorter ontothe optical recording medium 10 via an objective lens (not shown) havinga numerical aperture NA of 0.7 or more and it is more preferable thatλ/NA be equal to or smaller than 640 nm.

In this embodiment, a laser beam L having a wavelength λ of 405 nm isprojected onto the optical recording medium 10 via an objective lenshaving a numerical aperture NA of 0.85.

As a result, an alloy contained in the recording layer as a primarycomponent is melted at the region of the recording layer 14 irradiatedwith the laser beam L and the phase thereof is changed when the meltedalloy is solidified, whereby a record mark is formed and data arerecorded in the recording layer 14 of the optical recording medium 10.

On the other hand, in the case where data recorded in the recordinglayer 14 of the optical recording medium 10 are to be reproduced, alaser beam L having a predetermined power is projected onto therecording layer 14 via the light transmission layer 16, while theoptical recording medium 10 is being rotated, and the amount of thelaser beam L reflected by the recording layer 14 is detected, wherebydata recorded in the recording layer 14 of the optical recording medium10 are reproduced.

Each of FIGS. 3 to 6 is a diagram showing the waveform of a pulsepattern for modulating the power of the laser beam L in the case ofrecording data in the recording layer 14 of the optical recording medium10, where FIG. 3 shows a pulse pattern used in the case of recording 2Tsignals, FIG. 4 shows a pulse pattern used in the case of recording 3Tsignals, FIG. 5 shows a pulse pattern used in the case of recording 4Tsignals and FIG. 6 shows random signals used in the case of recordingone among a 5T signal to an 8T signal.

As shown in FIGS. 3 to 6, the power of the laser beam L is modulatedbetween two levels, a recording power Pw and a bottom power Pb wherePw>Pb.

The recording power Pw is set to a high level capable of melting andchanging the phase of an alloy contained in the recording layer 14 ofthe optical recording medium 10 when the laser beam L set to therecording power Pw is projected onto the recording layer 14. On theother hand, the bottom power Pb is set to an extremely low level atwhich a region of the recording layer 14 heated by irradiation with thelaser beam L set to the recording power Pw can be cooled duringirradiation with the laser beam L set to the bottom power Pb.

As shown in FIG. 3, in the case of recording a 2T signal in therecording layer 14 of the optical recording medium 10, the power of thelaser beam L is modulated to be increased from the bottom power Pb tothe recording power Pw at a time t11 and decreased from the recordingpower Pw to the bottom power Pb at a time t12 after passage of apredetermined time period t_(top).

Therefore, in the case of recording a 2T signal in the L0 informationrecording layer 20 or the L1 information recording layer 30 of theoptical recording medium 10, the number of a pulse having a level equalto the recording power Pw is set to be 1.

On the other hand, as shown in FIG. 4, in the case of recording a 3Tsignal in the recording layer 14 of the optical recording medium 10, thepower of the laser beam L is modulated so that it is increased from thebottom power Pb to the recording power Pw at a time t21, decreased fromthe recording power Pw to the bottom power Pb at a time t22 afterpassage of a predetermined time period t_(top), increased from thebottom power Pb to the recording power Pw at a time t23 after passage ofa predetermined time period t_(off) and decreased from the recordingpower Pw to the bottom power Pb at a time t24 after passage of apredetermined time period t_(lp).

Therefore, in the case of recording a 3T signal in the recording layer14 of the optical recording medium 10, the number of pulses each havinga level equal to the recording power Pw is set to be 2.

Further, as shown in FIG. 5, in the case of recording a 4T signal in therecording layer 14 of the optical recording medium 10, the power of thelaser beam L is modulated so that it is increased from the bottom powerPb to the recording power Pw at a time t31, decreased from the recordingpower Pw to the bottom power Pb at a time t32 after passage of apredetermined time period t_(top), increased from the bottom power Pb tothe recording power Pw at a time t33 after passage of a predeterminedtime period t_(off), decreased from the recording power Pw to the bottompower Pb at a time t34 after passage of a predetermined time periodt_(mp), increased from the bottom power Pb to the recording power Pw ata time t35 after passage of a predetermined time period t_(top) anddecreased from the recording power Pw to the bottom power Pb at a timet36 after passage of a predetermined time period t_(lp).

Therefore, in the case of recording a 4T signal in the recording layer14 of the optical recording medium 10, the number of pulses each havinga level equal to the recording power Pw is set to be 3.

Moreover, as shown in FIG. 6, in the case of recording one among a 5Tsignal to an 8T signal in the recording layer 14 of the opticalrecording medium 10, the power of the laser beam L is modulated so thatit is increased from the bottom power Pb to the recording power Pw at atime t41, held at the recording power Pw during the time period t_(top),the time periods t_(mp) and the time period t_(lp), held at the bottompower Pb during the time periods t_(off) and decreased from therecording power Pw to the bottom power Pb at a time t48.

Therefore, in the case of recording one among a 5T signal to a 8T signalin the recording layer 14 of the optical recording medium 10, the numberof pulses each having a level equal to the recording power Pw is set tobe 4 to 7.

When the recording layer 14 is irradiated with the laser beam L set tothe recording power Pw, an alloy contained in the recording layer 14 asa primary component is melted at a region of the recording layer 14irradiated with the laser beam L, and when it is irradiated with thelaser beam L set to the bottom power Pb, the melted alloy is solidifiedand the phase of the alloy is changed, whereby a record mark is formedand data are recorded in the recording layer 14.

Since the reflective coefficient with respect to a laser beam L of aregion of the recording layer 14 where the record mark is formed in thismanner and that of a region where no record mark is formed, namely, ablank region, are greatly different, data recorded in the recordinglayer 14 can be reproduced utilizing the difference in the reflectioncoefficients between the region of the recording layer 14 where therecord mark is formed and the blank region.

The length of the record mark and the length of the blank region betweenthe record mark and the neighboring record mark constitute data recordedin the recording layer 14. The record mark and the blank region areformed so as to have a length equal to an integral multiple of T, whereT is a length corresponding to one cycle of a reference clock. In thecase where 1,7 RLL modulation code is employed, record marks and blankregions having a length of 2T to 8T are formed.

According to this embodiment, since the recording layer 14 of theoptical recording medium 10 contains an alloy represented by a generalformula: (Ti_(x)M1 _(1−x))_(y)M2 _(1−y), where element M1 is Si or Al,element M2 is an element different from the element M1, x is equal to orlarger than 0.3 and equal to or smaller than 0.8, and y is equal to orlarger than 0.75 and equal to or smaller than 1 and since each of Ti, Siand Al contained as an indispensable component in the alloy contained inthe recording layer 14 and Si, Al and Fe contained in the alloy as anoptional component is one of the most commonplace elements on earth andputs only an extremely light load on the global environment, an opticalrecording medium 10 including a recording layer 14 containing an alloycontaining such elements can greatly lower the load placed the globalenvironment.

Further, according to this embodiment, since the content of Ti and Si orTi and Al contained as indispensable components in the alloy containedin the recording layer 14 is determined so that x is equal to or largerthan 0.3 and equal to or smaller than 0.8, it is possible to reproduce asignal having a high C/N ratio and decreased jitter and effectivelysuppress cross-talk of data.

FIG. 7 is a schematic cross-sectional view showing an optical recordingmedium which is another preferred embodiment of the present invention.

As shown in FIG. 7, the optical recording medium 30 according to thisembodiment includes a support substrate 31, a transparent intermediatelayer 32, a light transmission layer (protective layer) 33, an L0information recording layer 40 formed between the support substrate 31and the transparent intermediate layer 32, and an L1 informationrecording layer 50 formed between the transparent layer 32 and the lighttransmission layer 33.

The L0 information recording layer 40 and the L1 information recordinglayer 50 are information recording layers in which data are recorded,i.e., the optical recording medium 30 according to this embodimentincludes two information recording layers.

The L0 information recording layer 40 constitutes an informationrecording layer far from a light incident plane 33 a and is constitutedby laminating a reflective layer 41, a fourth dielectric layer 42, an L0recording layer 43 and a third dielectric layer 44 from the side of thesupport substrate 31.

On the other hand, the L1 information recording layer 50 constitutes aninformation recording layer close to the light incident plane 33 a andis constituted by laminating a reflective layer 51, a second dielectriclayer 52, an L1 recording layer 53 and a first dielectric layer 54 fromthe side of the support substrate 31.

The support substrate 31 serves as a support for ensuring the mechanicalstrength and thickness of about 1.2 mm required by the optical recordingmedium 30 and is formed in the same way as the support substrate 11 ofthe optical recording medium 10 shown in FIGS. 1 and 2.

As shown in FIG. 7, grooves 31 a and lands 31 b are alternately andspirally formed on the surface of the support substrate 31 so as to havea depth and a pitch similar to those of the optical recording medium 10shown in FIGS. 1 and 2. The grooves 31 a and/or lands 31 b serve as aguide track for the laser beam L when data are to be recorded in the L0information recording layer 40 or when data are to be reproduced fromthe L0 information recording layer 40.

The transparent intermediate layer 32 serves to space the L0 informationrecording layer 40 and the L1 information recording layer 50 apart by aphysically and optically sufficient distance.

As shown in FIG. 7, grooves 32 a and lands 32 b are alternately formedon the surface of the transparent intermediate layer 32. The grooves 32a and/or lands 32 b formed on the surface of the transparentintermediate layer 32 serve as a guide track for the laser beam L whendata are to be recorded in the L1 layer 50 or when data are to be

The depth of the groove 32 a and the pitch of the grooves 32 a can beset to be substantially the same as those of the grooves 31 a formed onthe surface of the support substrate 31.

It is preferable to form the transparent intermediate layer 32 so as tohave a thickness of 5 μm to 50 μm and it is more preferable to form itso as to have a thickness of 10 μm to 40 μm.

The material for forming the transparent intermediate layer 32 is notparticularly limited and an ultraviolet ray curable acrylic resin ispreferably used for forming the transparent intermediate layer 32.

It is necessary for the transparent intermediate layer 32 to havesufficiently high light transmittance since the laser beam L passesthrough the transparent intermediate layer 32 when data are to berecorded in the L0 information recording layer 40 and data recorded inthe L0 information recording layer 40 are to be reproduced.

The transparent intermediate layer 32 is preferably formed by a 2Pprocess using a stamper but the transparent intermediate layer 32 may beformed by other processes.

The light transmission layer 33 serves to transmit the laser beam L andthe light incident plane 33 a is constituted by one of the surfacesthereof.

The light transmission layer 33 is formed in the same way as the lighttransmission layer 16 of the optical recording medium 10 shown in FIGS.1 and 2.

The L0 recording layer 43 included in the L0 information recording layer40 contains an alloy represented by the above mentioned general formula:(Ti_(x)M1 _(1−x))_(y)M2 _(1−y).

Similarly, the L1 recording layer 53 included in the L1 informationrecording layer 50 contains an alloy represented by the above mentionedgeneral formula: (Ti_(x)M1 _(1−x))_(y)M2 _(1−y).

Each of the reflective layer 41 included in the L0 information recordinglayer 40 and the reflective layer 51 included in the L1 informationrecording layer 50 is formed in the same way as the reflective layer 12of the optical recording medium 10 shown in FIGS. 1 and 2.

Each of the fourth dielectric layer 42 and the third dielectric layer 44included in the L0 information recording layer 40 and the seconddielectric layer 52 and the first dielectric layer 54 included in the L1information recording layer 50 is formed in the same way as the firstdielectric layer 15 or the second dielectric layer 13 of the opticalrecording medium 10 shown in FIGS. 1 and 2.

Each of the reflective layer 41, the fourth dielectric layer 42, the L0recording layer 43 and the third dielectric layer 44 included in the L0information recording layer 40, and the reflective layer 51, the seconddielectric layer 52, the L1 recording layer 53 and the first dielectriclayer 54 included in the L1 information recording layer 50 can be formedby a vapor growth process using chemical species containing elements forforming it. Illustrative examples of the vapor growth processes includea sputtering process, vacuum deposition process and the like and thesputtering process is preferably used for forming them.

When data are to be recorded in the L0 recording layer 43 included inthe L0 information recording layer 40 of the optical recording medium30, a laser beam L set to the recording power Pw is focused onto the L0recording layer 43 via the light transmission layer 33. As a result, analloy contained in the L0 recording layer 43 as a primary component ismelted at the region of the L0 recording layer 43 irradiated with thelaser beam L and when the laser beam L is set to the bottom power Pb,the melted alloy is solidified and the phase of the alloy is changed,whereby a record mark is formed and data are recorded in the L0recording layer 43.

On the other hand, when data are to be recorded in the L1 recordinglayer 53 included in the L1 information recording layer 50 of theoptical recording medium 30, a laser beam L set to the recording powerPw is focused onto the L1 recording layer 53 via the light transmissionlayer 33. As a result, an alloy contained in the L1 recording layer 53as a primary component is melted at the region of the L1 recording layer53 irradiated with the laser beam L and when the laser beam L is set tothe bottom power Pb, the melted alloy is solidified and the phase of thealloy is changed, whereby a record mark is formed and data are recordedin the L1 recording layer 53.

When data recorded in the L0 recording layer 43 included in the L0information recording layer 40 of the optical recording medium 30 are tobe reproduced, a laser beam L set to a reproducing power is focused ontothe L0 recording layer 43 via the light transmission layer 33 and theamount of the laser beam L reflected by the L0 recording layer 43 isdetected.

On the other hand, when data recorded in the L1 recording layer 53included in the L1 information recording layer 50 of the opticalrecording medium 30 are to be reproduced, a laser beam L set to be areproducing power is focused onto the L1 recording layer 53 via thelight transmission layer 33 and the amount of the laser beam L reflectedby the L1 recording layer 53 is detected.

According to this embodiment, each of the L0 recording layer 43 and theL1 recording layer 53 contains an alloy represented by a generalformula: (Ti_(x)M1 _(1−x))_(y)M2 _(1−y), where element M1 is Si or Al,element M2 is an element different from the element M1, x is equal to orlarger than 0.3 and equal to or smaller than 0.8, and y is equal to orlarger than 0.75 and equal to or smaller than 1 and since each of Ti, Siand Al contained as an indispensable component in the alloy contained inthe recording layer 14 and Si, Al and Fe contained in the alloy as anoptional component is one of the most commonplace elements on earth andputs only an extremely light load on the global environment, an opticalrecording medium 10 including a recording layer 14 containing an alloycontaining such elements can greatly lower the load placed the globalenvironment.

Further, according to this embodiment, since the content of Ti and Si orTi and Al contained as indispensable components in the alloy containedin each of the L0 recording layer 43 and the L1 recording layer 53 isdetermined so that x is equal to or larger than 0.3 and equal to orsmaller than 0.8, it is possible to reproduce a signal having a high C/Nratio and decreased jitter and effectively suppress cross-talk of data.

WORKING EXAMPLES AND COMPARATIVE EXAMPLES

Hereinafter, working examples will be set out in order to furtherclarify the advantages of the present invention.

Working Example 1

An optical recording medium sample #1-1 was fabricated in the followingmanner.

A disk-like polycarbonate substrate having a thickness of 1.1 mm and adiameter of 120 mm and formed with grooves and lands on the surfacethereof was first fabricated by an injection molding process so that thetrack pitch (groove pitch) was equal to 0.32 μm.

Then, the polycarbonate substrate was set on a sputtering apparatus anda reflective layer consisting of an alloy containing Ag, Pd and Cu andhaving a thickness of 100 nm, a second dielectric layer containing amixture of ZnS and SiO₂ and having a thickness of 25 nm, a recordinglayer containing an alloy represented by a composition formula:Ti_(x)Si_(1−x) and having a thickness of 10 nm and a first dielectricfilm containing the mixture of ZnS and SiO₂ and having a thickness of 20nm were sequentially formed on the surface of the polycarbonatesubstrate on which the grooves and lands were formed, using thesputtering process.

The mole ratio of ZnS to SiO₂ in the mixture of ZnS and SiO₂ containedin the first dielectric layer and the second dielectric layer was 80:20.

Further, the composition of the alloy contained in the recording layerwas determined so that the value of x in the composition formula:Ti_(x)Si_(1−x) was equal to 0.2 (20 atomic %).

Further, the polycarbonate substrate formed with the reflective layer,the second dielectric layer, the recording layer and the firstdielectric layer on the surface thereof was set on a spin coatingapparatus and the first dielectric layer was coated using the spincoating method with a resin solution prepared by dissolving acrylicultraviolet ray curable resin in a solvent to form a coating layer andthe coating layer was irradiated with ultraviolet rays, thereby curingthe acrylic ultraviolet ray curable resin to form a light transmissionlayer having a thickness of 100 μm.

Thus, the optical recording medium sample #1-1 was fabricated.

Further, optical recording medium samples #1-2 to #1-5 were fabricatedin the same way as the optical recording medium sample #1-1 except thatthe value of x in the composition formula: Ti_(x),Si_(1−x), was stepwiseincreased up to 1 (100 atomic %) to form recording layers.

Each of the optical recording medium samples #1-1 to #1-5 was set in anoptical recording medium evaluation apparatus “DDU1000 ” (Product Name)manufactured by Pulstec Industrial Co., Ltd. and a laser beam having awavelength of 405 nm whose power was modulated in accordance with thepulse pattern shown in FIG. 3 was focused onto the recording layer usingan objective lens whose numerical aperture was 0.85 via the lighttransmission layer while each of the samples was rotated at a linearvelocity of 5.3 m/sec, thereby recording a random signal including a 2Tsignal to an 8T signal therein in the 1,7 RLL Modulation Code.

The recording power of the laser beam was set to 7.0 mW, while thebottom power of the laser beam was fixed at 0.1 mW.

Then, each of the optical recording medium samples #1-1 to #1-5 was setin the above mentioned optical recording medium evaluation apparatus anda laser beam having a wavelength of 405 nm was focused onto therecording layer of each sample using an objective lens whose numericalaperture was 0.85 via the light transmission layer while each sample wasrotated at a linear velocity of 5.3 m/sec, thereby reproducing a signalrecorded in the recording layer and clock jitter of the reproduced wasmeasured. The reproducing power of the laser beam was set to 0.35 mW.

The fluctuation σ of the reproduced signal was measured using a timeinterval analyzer and the clock jitter was calculated as σ/Tw, where Twwas one clock period.

Further, similarly to the above, a random signal was recorded in each ofthe optical recording medium samples #1-1 to #1-5 while increasing therecording power of the laser beam in increments of 0.2 mW up to 10.0 mW,thereby reproducing the random signal from each sample and measuringclock jitter of the reproduced signal similarly to the above.

The lowest clock jitter was determined from among the thus measuredclock jitters and the recording power at which the clock jitter of thereproduced signal was lowest was determined as an optimum recordingpower of the laser beam.

Then, each of the optical recording medium samples #1-1 to #1-5 was setin the above mentioned optical recording medium evaluation apparatus anda 2T signal in the 1,7 RLL Modulation Code was recorded in the recordinglayer of each sample in the same manner as that of recording the randomsignal in the recording layer of each sample except that the recordingpower of the laser beam was set to the optimum recording power.

Further, each of the optical recording medium samples #1-1 to #1-5 wasset in the above mentioned optical recording medium evaluation apparatusand in the same manner as that of reproducing the random signal from therecording layer of each sample, the 2T signal recorded in the recordinglayer of each sample was reproduced, thereby measuring the C/N ratio ofthe reproduced signal.

The results of the measurement are shown in FIG. 8.

Then, each of the optical recording medium samples #1-1 to #1-5 was setin the above mentioned optical recording medium evaluation apparatus andan 8T signal in the 1,7 RLL Modulation Code was recorded in therecording layer of each sample in the same manner as that of recordingthe random signal in the recording layer of each sample except that therecording power of the laser beam was set to the optimum recordingpower.

Further, each of the optical recording medium samples #1-1 to #1-5 wasset in the above mentioned optical recording medium evaluation apparatusand in the same manner as that of reproducing the random signal from therecording layer of each sample, the 8T signal recorded in the recordinglayer of each sample was reproduced, thereby measuring the C/N ratio ofthe reproduced signal.

The results of the measurement are shown in FIG. 8.

As shown in FIG. 8, it was found that in the case where the value of xin the composition formula: Ti_(x)Si_(1−x) was 0.3 (30 atomic %) to 0.8(80 atomic %), the C/N ratio of the signal obtained by reproducing the2T signal was equal to or higher than 40 dB and the C/N ratio of thesignal obtained by reproducing the 8T signal was equal to or higher than45 dB and that each sample could be practically used as an opticalrecording medium.

Further, it was found that in the case where the value of x in thecomposition formula: Ti_(x)Si_(1−x) was 0.4 (40 atomic %) to 0.6 (60atomic %), both the C/N ratio of the signal obtained by reproducing the2T signal and the C/N ratio of the signal obtained by reproducing the 8Tsignal became higher and that in the case where the value of x was about0.5 (50 atomic %), and both the C/N ratio of the signal obtained byreproducing the 2T signal and the C/N ratio of a signal obtained byreproducing the 8T signal became maximum.

Working Example 2

In the same manner as in Working Example 1, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #1-1 to #1-5 by setting therecording power of the laser beam to the optimum recording power. Then,the thus recorded random signal was reproduced from each of the opticalrecording medium samples #1-1 to #1-5 and clock jitter of the reproducedsignal was measured.

The results of the measurement are shown in FIG. 9.

In FIG. 9, the curve A1 shows clock jitter (single jitter) of areproduced signal obtained from a track located between tracks in whichno data were reproduced and the curve A2 shows clock jitter (crossjitter) of a reproduced signal obtained from a track located betweentracks in which data were recorded.

As shown in FIG. 9, it was found that both single jitter and crossjitter were high in the case where the value of x in the compositionformula: Ti_(x)Si_(1−x) was smaller than 0.3 (30 atomic %). It wasfurther found that in the case where the value of x was 0.4 (40 atomic%) to 0.6 (60 atomic %), the difference in values between single jitterand cross jitter was small and that that in the case where the value ofx was about 0.5 (50 atomic %), the difference in values between singlejitter and cross jitter was very small.

Therefore, it was found that in order to improve cross-talkcharacteristics of an optical recording medium, it was preferable todetermine the composition of the alloy contained in the recording layerso that the value of x in the composition formula: Ti_(x)Si_(1−x) was0.4 (40 atomic %) to 0.6 (60 atomic %) and that it was particularlypreferable to determined the composition of the alloy contained in therecording layer so that the value of x was about 0.5.

Working Example 3

An optical recording medium sample #3-1 was fabricated in the samemanner as in Working Example 1 except that a recording layer containingan alloy represented by a composition formula:(Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was formed.

The composition of the alloy contained in the recording layer wasdetermined so that the value of y in the composition formula:(Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was equal to 0.67 (67 atomic %).

Further, optical recording medium samples #3-2 to #3-4 were fabricatedin the same way as the optical recording medium sample #3-1 except thatthe value of y in the composition formula:(Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was stepwise increased up to 1 (100atomic %) to form recording layers.

Further, each of the optical recording medium samples #3-1 to #3-4 wasset in the above mentioned optical recording medium evaluation apparatusand in the same manner as in Working Example 1, a random signalincluding a 2T signal to an 8T signal in the 1,7 RLL Modulation Code wasrecorded in each of the optical recording medium samples #3-1 to #3-4using a laser beam whose recording power was set to 7.0 mW. Then, in thesame manner as in Working Example 1, the thus recorded random signal wasreproduced from each of the optical recording medium samples #3-1 to#3-4 and clock jitter of the reproduced signal was measured.

Further, similarly to the above, a random signal was recorded in each ofthe optical recording medium samples #3-1 to #3-4 while increasing therecording power of the laser beam in increments of 0.2 mW up to 10.0 mW,thereby reproducing the random signal from each sample and measuringclock jitter of the reproduced signal similarly to the above.

The lowest clock jitter was determined from among the thus measuredclock jitters and the recording power at which the clock jitter of thereproduced signal was lowest was determined as an optimum recordingpower of the laser beam.

Further, a 2T signal was recorded in each of the optical recordingmedium samples #3-1 to #3-4 using a laser beam whose recording power wasset to the optimum recording power in the same manner as that ofrecording the random signal in the recording layer of each sample.

Then, in the same manner as that of reproducing the random signal fromthe recording layer of each sample, the 2T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #3-1 to #3-4, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 10.

Further, each of the optical recording medium samples #3-1 to #3-4 wasset in the above mentioned optical recording medium evaluation apparatusand an 8T signal in the 1,7 RLL Modulation Code was recorded in each ofthe optical recording medium samples #3-1 to #3-4 using a laser beamwhose power was set to the optimum recording power in the same manner asthat of recording the 2T signal in the recording layer of each sample.

Then, in the same manner as that of reproducing the 2T signal from therecording layer of each sample, the 8T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #3-1 to #3-4, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 10.

As shown in FIG. 10, it was found that in the case where the value of yin the composition formula: (Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was 0.75 (75atomic %) to 1 (100 atomic %), both the C/N ratio of the signal obtainedby reproducing the 2T signal and the C/N ratio of the signal obtained byreproducing the 8T signal were substantially constant and that in thecase where the value of y in the composition formula:(Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was smaller than 0.75 (75 atomic %), boththe C/N ratio of the signal obtained by reproducing the 2T signal andthe C/N ratio of the signal obtained by reproducing the 8T signal wereextremely low.

Therefore, it was found that in the case where the value of y in thecomposition formula: (Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was equal to orlarger than 0.75 (75 atomic %), the C/N ratio of the reproduced signalwas hardly influenced by any Al contained in the alloy.

Working Example 4

In the same manner as in Working Example 3, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #3-1 to #3-4 by setting therecording power of the laser beam to the optimum recording power. Then,the thus recorded random signal was reproduced from each of the opticalrecording medium samples #3-1 to #3-4 and clock jitter of the reproducedsignal was measured.

The results of the measurement are shown in FIG. 11.

In FIG. 11, the curve B1 shows clock jitter (single jitter) of areproduced signal obtained from a track located between tracks in whichno data were reproduced and the curve B2 shows clock jitter (crossjitter) of a reproduced signal obtained from a track located betweentracks in which data were recorded.

As shown in FIG. 11, it was found that in the case where the value of yin the composition formula: (Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was 0.75 (75atomic %) to 1 (100 atomic %), both single jitter and cross jitter weresubstantially constant and that in the case where the value of y in thecomposition formula: (Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was smaller than0.75 (75 atomic %), both single jitter and cross jitter were extremelyhigh.

Therefore, it was found that in the case where the value of y in thecomposition formula: (Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was equal to orlarger than 0.75 (75 atomic %), single jitter and cross jitter of areproduced signal were hardly influenced by any Al contained in thealloy.

Working Example 5

An optical recording medium sample #5-1 was fabricated in the samemanner as in Working Example 1 except that a recording layer containingan alloy represented by a composition formula: Ti_(x)Al_(1−x) and afirst dielectric layer having a thickness of 35 nm was formed.

The composition of the alloy contained in the recording layer wasdetermined so that the value of x in the composition formula:Ti_(x)Al_(1−x) was equal to 0.15 (15 atomic %).

Further, optical recording medium samples #5-2 to #5-5 were fabricatedin the same way as the optical recording medium sample #5-1 except thatthe value of x in the composition formula: Ti_(x)Al_(1−x) was stepwiseincreased up to 1 (100 atomic %) to form recording layers.

Then, each of the optical recording medium samples #5-1 to #5-5 was setin the above mentioned optical recording medium evaluation apparatus andin the same manner as in Working Example 1, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #5-1 to #5-5 using a laserbeam whose recording power was set to 7.0 mW. Then, the thus recordedrandom signal was reproduced from each of the optical recording mediumsamples #5-1 to #5-5 and clock jitter of the reproduced signal wasmeasured.

Further, similarly to the above, a random signal was recorded in each ofthe optical recording medium samples #5-1 to #5-5 while increasing therecording power of the laser beam in increments of 0.2 mW up to 10.0 mW,thereby reproducing the random signal from each sample and measuringclock jitter of the reproduced signal similarly to the above.

The lowest clock jitter was determined from among the thus measuredclock jitters and the recording power at which the clock jitter of thereproduced signal was lowest was determined as an optimum recordingpower of the laser beam.

Further, a 2T signal was recorded in each of the optical recordingmedium samples #5-1 to #5-5 using a laser beam whose recording power wasset to the optimum recording power in the same manner as that ofrecording the random signal in the recording layer of each sample .

Then, in the same manner as that of reproducing the random signal fromthe recording layer of each sample, the 2T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #5-1 to #5-5, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 12.

Further, each of the optical recording medium samples #5-1 to #5-5 wasset in the above mentioned optical recording medium evaluation apparatusand an 8T signal in the 1,7 RLL Modulation Code was recorded in each ofthe optical recording medium samples #5-1 to #5-5 using a laser beamwhose recording power was set to the optimum recording power in the samemanner as that of recording the random signal in the recording layer ofeach sample.

Then, in the same manner as that of reproducing the random signal fromthe recording layer of each sample, the 8T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #5-1 to #5-5, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 12.

As shown in FIG. 12, it was found that in the case where the value of xin the composition formula: Ti_(x)Al_(1−x) was 0.3 (30 atomic %) to 0.8(80 atomic %), the C/N ratio of the signal obtained by reproducing the2T signal was equal to or higher than 40 dB and the C/N ratio of thesignal obtained by reproducing the 8T signal was equal to or higher than45 dB and that each sample could be practically used as an opticalrecording medium.

Further, it was found that in the case where the value of x in thecomposition formula: Ti_(x)Al_(1−y) was 0.4 (40 atomic %) to 0.6 (60atomic %), both the C/N ratio of the signal obtained by reproducing the2T signal and the C/N ratio of the signal obtained by reproducing the 8Tsignal became higher and that in the case where the value of x was about0.5 (50 atomic %), and both the C/N ratio of the signal obtained byreproducing the 2T signal and the C/N ratio of the signal obtained byreproducing the 8T signal became maximum.

Working Example 6

In the same manner as in Working Example 5, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #5-1 to #5-5 by setting therecording power of the laser beam to the optimum recording power. Then,the thus recorded random signal was reproduced from each of the opticalrecording medium samples #5-1 to #5-5 and clock jitter of the reproducedsignal was measured.

The results of the measurement are shown in FIG. 13.

In FIG. 13, the curve Cl shows clock jitter (single jitter) of areproduced signal obtained from a track located between tracks in whichno data were reproduced and the curve C2 shows clock jitter (crossjitter) of a reproduced signal obtained from a track located betweentracks in which data were recorded.

As shown in FIG. 13, it was found that in the case where the value of xin the composition formula: Ti_(x)Al_(1−x) was less than 0.3 (30 atomic%), both single jitter and cross jitter were extremely high and that inthe case where the value of x in the composition formula: Ti_(x)Al_(1−x)was equal to or more than 0.4 (40 atomic %) and equal to or less than0.6 (60 atomic %), the difference between single jitter and cross jitterwas small. It was further found that in the case where the value of x inthe composition formula: Ti_(x)Al_(1−x) was about 0.5, the differencebetween single jitter and cross jitter was extremely small.

Therefore, it was found that in order to improve cross-talkcharacteristics of an optical recording medium, it was preferable todetermine the composition of the alloy contained in the recording layerso that the value of x in the composition formula: Ti_(x)Al_(1−x) was0.4 (40 atomic %) to 0.6 (60 atomic %) and that it was particularlypreferable to determine the composition of the alloy contained in therecording layer so that the value of x was about 0.5.

Working Example 7

An optical recording medium sample #7-1 was fabricated in the samemanner as in Working Example 1 except that a recording layer containingan alloy represented by a composition formula:(Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was formed.

The composition of the alloy contained in the recording layer wasdetermined so that the value of y in the composition formula:(Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was equal to 0.67 (67 atomic %).

Further, optical recording medium samples #7-2 and #7-3 were fabricatedin the same way as the optical recording medium sample #7-1 except thatthe value of y in the composition formula:(Ti_(0.5)Si_(0.5))_(y)Al_(1−y) was stepwise increased up to 1 (100atomic %) to form recording layers.

Then, each of the optical recording medium samples #7-1 to #7-3 was setin the above mentioned optical recording medium evaluation apparatus andin the same manner as in Working Example 1, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #7-1 to #7-3 using a laserbeam whose recording power was set to 7.0 mW. Then, the thus recordedrandom signal was reproduced from each of the optical recording mediumsamples #7-1 to #7-3 and clock jitter of the reproduced signal wasmeasured.

Further, similarly to the above, a random signal was recorded in each ofthe optical recording medium samples #7-1 to #7-3 while increasing therecording power of the laser beam in increments of 0.2 mW up to 10.0 mW,thereby reproducing the random signal from each sample and measuringclock jitter of the reproduced signal similarly to the above.

The lowest clock jitter was determined from among the thus measuredclock jitters and the recording power at which the clock jitter of thereproduced signal was lowest was determined as an optimum recordingpower of the laser beam.

Further, a 2T signal was recorded in each of the optical recordingmedium samples #7-1 to #7-3 using a laser beam whose recording power wasset to the optimum recording power in the same manner as that ofrecording the random signal in the recording layer of each sample.

Then, in the same manner as that of reproducing the random signal fromthe recording layer of each sample, the 2T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #7-1 to #7-3, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 14.

Further, each of the optical recording medium samples #7-1 to #7-3 wasset in the above mentioned optical recording medium evaluation apparatusand an 8T signal in the 1,7 RLL Modulation Code was recorded in each ofthe optical recording medium samples #7-1 to #7-3 using a laser beamwhose recording power was set to the optimum recording power in thesimilar manner as that of recording the random signal in the recordinglayer of each sample.

Then, in the same manner as that of reproducing the random signal fromthe recording layer of each sample, the 8T signal recorded using a laserwhose power was set to the optimum recording power was reproduced fromeach of the optical recording medium samples #7-1 to #7-3, therebymeasuring the C/N ratio of the reproduced signal.

The results of the measurement are shown in FIG. 14.

As shown in FIG. 14, it was found that in the case where the value of yin the composition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was 0.75 (75atomic %) to 1 (100 atomic %), both the C/N ratio of the signal obtainedby reproducing the 2T signal and the C/N ratio of the signal obtained byreproducing the 8T signal decreased slightly as the value of y decreasedbut that the C/N ratio of the signal obtained by reproducing the 2Tsignal was substantially equal to or higher than 40 dB and the C/N ratioof the signal obtained by reproducing the 8T signal was equal to orhigher than 50 dB.

On the other hand, it was found that in the case where the value of y inthe composition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was smaller than0.75 (75 atomic %) to 1 (100 atomic %), both the C/N ratio of the signalobtained by reproducing the 2T signal and the C/N ratio of the signalobtained by reproducing the 8T signal decreased as the value of ydecreased,.

Therefore, it was found that in the case where the value of y in thecomposition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was equal to orlarger than 0.75 (75 atomic %), the C/N ratio of a reproduced signal wasnot much influenced by any Si contained in the alloy.

Working Example 8

In the same manner as in Working Example 7, a random signal including a2T signal to an 8T signal in the 1,7 RLL Modulation Code was recorded ineach of the optical recording medium samples #7-1 to #7-3 by setting therecording power of the laser beam to the optimum recording power. Then,the thus recorded random signal was reproduced from each of the opticalrecording medium samples #7-1 to #7-3 and clock jitter of the reproducedsignal was measured.

The results of the measurement are shown in FIG. 15.

In FIG. 15, the curve D1 shows clock jitter (single jitter) of areproduced signal obtained from a track located between tracks in whichno data were reproduced and the curve D2 shows clock jitter (crossjitter) of a reproduced signal obtained from a track located betweentracks in which data were recorded.

As shown in FIG. 15, it was found that in the case where the value of yin the composition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was 0.75 (75atomic %) to 1 (100 atomic %), decreasing value of y was accompanied byslight increase in both single jitter and cross jitter but no markedincrease in single jitter and cross jitter was observed.

To the contrary, it was found that in the case where the value of y inthe composition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was smaller than0.75 (75 atomic %) to 1 (100 atomic %), decreasing value of y wasaccompanied by an abrupt increase in both single jitter and crossjitter.

Therefore, it was found that in the case where the value of y in thecomposition formula: (Ti_(0.5)Al_(0.5))_(y)Si_(1−y) was equal to orlarger than 0.75 (75 atomic %), single jitter and cross jitter of areproduced signal were not much influenced by any Si contained in thealloy.

The present invention has thus been shown and described with referenceto specific embodiments and working examples. However, it should benoted that the present invention is in no way limited to the details ofthe described arrangements but changes and modifications may be madewithout departing from the scope of the appended claims.

For example, in the optical recording medium 10 shown in FIGS. 1 and 2,although the recording layer 14 is sandwiched by the second dielectriclayer 23 and the first dielectric layer 15, only one of the seconddielectric layer 23 and the first dielectric layer 15 may be formed tobe adjacent to the recording layer 14. Similarly, in the opticalrecording medium 30 shown in FIG. 7, each of the L0 informationrecording layer 40 and the L1 information recording layer 50 may includea single dielectric layer.

Moreover, although the optical recording medium 10 shown in FIGS. 1 and2 includes the reflective layer 12 on the support substrate 11, in thecase where the difference in reflection coefficients between a region ofthe recording layer 14 where a record mark is formed and a blank regionis great, the reflective layer 12 may be omitted.

Further, in the above described embodiments, although each of thereflective layer 12, the reflective layer 41 and the reflective layer 51is constituted as a single layer, each of the reflective layer 12, thereflective layer 41 and the reflective layer 51may have a multi-layeredstructure.

Furthermore, in the embodiment shown in FIG. 7, the L1 informationrecording layer 50 includes a reflective layer 51, but since a laserbeam L passes through the L1 information recording layer 50 when thelaser beam L is projected onto the L0 information recording layer 40,the L1 information recording layer 50 may be provided with no reflectivelayer or an extremely thin reflective layer in order to increase thelight transmittance of the L1 information recording layer 50.

Moreover, although the optical recording medium 10 includes the singlerecording layer 14 as an information recording layer in the embodimentshown in FIGS. 1 and 2 and the optical recording medium 30 includes theL0 information recording layer 40 and the L1 information recording layer50 in the embodiment shown in FIG. 7, an optical recording medium mayinclude three or more information recording layer.

Further, the optical recording medium 10 includes the light transmissionlayer 16 and is constituted so that a laser beam L is projected onto therecording layer 14 via the light transmission layer 16 in the embodimentshown in FIGS. 1 and 2, and the optical recording medium 30 includes thelight transmission layer 33 and is constituted so that a laser beam L isprojected onto the L1 information recording layer 50 or the L0information recording layer 40 via the light transmission layer 33 inthe embodiment shown in FIG. 7. However, the present invention is notlimited to optical recording media having such configurations and theoptical recording medium may include a substrate formed of a lighttransmittable material and be constituted so that a laser beam L isprojected onto the recording layer 14, or the L1 information recordinglayer 50 or the L0 information recording layer 40 via the substrate.

According to the present invention, it is possible to provide an opticalrecording medium including a recording layer formed of materials whichapply minimal load to the global environment.

Further, according to the present invention, it is possible to provide amethod for manufacturing an optical recording medium including arecording layer formed of materials which apply minimal load to theglobal environment.

Furthermore, according to the present invention, it is possible toprovide a target used for a sputtering process, which can form arecording layer of an optical recording medium of materials that placeminimal load on the global environment.

1. An optical recording medium comprising a recording layer containing an alloy represented by a general formula: (Ti_(x)M1 _(x))_(y)M2 _(y), where element M1 is Si or Al, element M2 is an element different from the element M1, x is equal to or larger than 0.3 and equal to or smaller than 0.8, and y is equal to or larger than 0.75 and equal to or smaller than
 1. 2. An optical recording medium in accordance with claim 1, wherein the element M2 is selected from the group consisting of Si, Al and Fe.
 3. An optical recording medium in accordance with claim 1, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6.
 4. An optical recording medium in accordance with claim 2, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6.
 5. An optical recording medium in accordance with claim 1, which further comprises a dielectric layer on at least one side of the recording layer.
 6. An optical recording medium in accordance with claim 2, which further comprises a dielectric layer on at least one side of the recording layer.
 7. An optical recording medium in accordance with claim 3, which further comprises a dielectric layer on at least one side of the recording layer.
 8. An optical recording medium in accordance with claim 1, which further comprises dielectric layers on opposite sides of the recording layer.
 9. An optical recording medium in accordance with claim 2, which further comprises dielectric layers on opposite sides of the recording layer.
 10. An optical recording medium in accordance with claim 3, which further comprises dielectric layers on opposite sides of the recording layer.
 11. A method for manufacturing an optical recording medium comprising of a step of forming a recording layer of an optical recording medium by a sputtering process using a target that contains an alloy represented by a general formula: (Ti_(x′)M1 _(x′))_(y′M2) _(y′), where element M1 is Si or Al, element M2 is an element different from the element M1, x′ is equal to or lager than 0.37 and equal to or smaller than 0.85 and y′ is equal to or lager than 0.75 and equal to or smaller than
 1. 12. A method for manufacturing an optical recording medium in accordance with claim 11, wherein the element M2 is selected from the group consisting of Si, Al and Fe.
 13. A method for manufacturing an optical recording medium in accordance with claim 11, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6.
 14. A method for manufacturing an optical recording medium in accordance with claim 12, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6.
 15. A target used for a sputtering process that contains an alloy represented by a general formula: (Ti_(x′)M1 _(x′))_(y′)M2 _(1−y′), where element M1 is Si or Al, element M2 is an element different from the element M1, x′ is equal to or lager than 0.37 and equal to or smaller than 0.85 and y′ is equal to or lager than 0.75 and equal to or smaller than
 1. 16. A target for a sputtering process in accordance with claim 15, wherein the element M2 is selected from the group consisting of Si, Al and Fe.
 17. A target for a sputtering process in accordance with claim 15, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6.
 18. A target for a sputtering process in accordance with claim 16, wherein x is equal to or larger than 0.4 and equal to or smaller than 0.6. 